U.S. patent number 5,467,232 [Application Number 08/036,280] was granted by the patent office on 1995-11-14 for magnetic recording and reproducing method using phase discrimination and apparatus therefor.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Yosuke Hori, Yasuhide Ouchi, Naoki Sato, Hideki Sawaguchi.
United States Patent |
5,467,232 |
Ouchi , et al. |
November 14, 1995 |
Magnetic recording and reproducing method using phase
discrimination and apparatus therefor
Abstract
In a phase discrimination signal processing system in the signal
reproduction of a magnetic recording and reproducing apparatus,
instead of differentiation of a reproduced signal, amplitude
discrimination automatic equalization is effected for an isolated
waveform at a phase discrimination point corresponding to an
isolated magnetization reversal reproduced by a magnetic head such
that an amplitude at each discrimination time other than a peak
point is zero to effect phase discrimination of the signal
waveform.
Inventors: |
Ouchi; Yasuhide (Kodaira,
JP), Sato; Naoki (Kokubunji, JP),
Sawaguchi; Hideki (Kodaira, JP), Hori; Yosuke
(Hiratsuka, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
13297152 |
Appl.
No.: |
08/036,280 |
Filed: |
March 24, 1993 |
Foreign Application Priority Data
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Mar 24, 1992 [JP] |
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4-065789 |
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Current U.S.
Class: |
360/65; 360/46;
360/51; 375/229; G9B/20.01; G9B/5.033 |
Current CPC
Class: |
G11B
5/09 (20130101); G11B 20/10009 (20130101); H04L
25/03038 (20130101) |
Current International
Class: |
G11B
5/09 (20060101); G11B 20/10 (20060101); H04L
25/03 (20060101); H04L 7/02 (20060101); G11B
005/035 (); G11B 005/09 (); G11B 027/10 (); H03H
007/30 () |
Field of
Search: |
;360/45,46,51,65
;375/12,11,14,101 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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57-88511 |
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Jun 1982 |
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JP |
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62-42368 |
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Feb 1987 |
|
JP |
|
Primary Examiner: Psitos; Aristotelis
Assistant Examiner: Kim; W. Chris
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus
Claims
What is claimed is:
1. A magnetic recording and reproducing method using a phase
discrimination system, said method comprising the steps of:
detecting an output waveform corresponding to a magnetization
reversal recorded on a magnetic recording medium;
producing a Nyquist waveform having a sampling time with a phase
discrimination time interval (T) based on said output waveform;
producing a waveform staggered from said Nyquist waveform by an
integral multiple of the phase discrimination time interval (T) and
of opposite polarity to said Nyquist waveform;
producing from said Nyquist waveform and said staggered waveform a
detection waveform having zero amplitude at phase discrimination
times corresponding to bit "1" of said output waveform and non-zero
amplitude at phase discrimination times corresponding to bit "0" of
said output waveform and having zero amplitude in said output
waveform at other phase discrimination times;
producing a gating output for extracting zero-crossing points of
said detection waveform from said Nyquist waveform; and
detecting a reproduced signal from the zero-crossing points of said
detection waveform based on said detection waveform and said gating
output.
2. A magnetic recording and reproducing method according to claim 1
wherein said output waveform is obtained by gain-controlling and
low-pass-filtering a waveform obtained from the magnetic recording
medium.
3. A magnetic recording and reproducing apparatus using a phase
discrimination system, said apparatus comprising:
means for detecting an output waveform corresponding to a
magnetization reversal recorded on a magnetic recording medium;
means for generating a Nyquist waveform having a sampling time with
a phase discrimination time interval (T) based on said output
waveform;
means for generating a waveform staggered from said Nyquist
waveform by an integral multiple of said phase discrimination time
interval (T) and of opposite polarity to said Nyquist waveform;
means for producing from said Nyquist waveform and said staggered
waveform a detection waveform having zero amplitude at phase
discrimination times corresponding to bit "1" of said output
waveform and non-zero amplitude at phase discrimination times
corresponding to bit "0" of said output waveform and having zero
amplitude in said output waveform at other phase discrimination
times;
means for producing a gating output for extracting zero-crossing
points of said detection waveform from said Nyquist waveform;
and
means for detecting a reproduced signal from the zero-crossing
points of said detection waveform based on said detection waveform
and said gating output.
4. A magnetic recording and reproducing method for reproducing a
digitally recorded signal by using a phase discrimination system,
said method comprising the steps of:
(a) applying a reproduced output waveform corresponding to an
isolated magnetization reversal reproduced by a magnetic head to a
phase discrimination transversal equalizer to transform the
reproduced output waveform to a dy-bit waveform which is a waveform
for a zero-crossing detection; and
(b) discriminating a zero-crossing point of said dy-bit waveform as
bit "1";
wherein step (a) comprises adding a plurality of Nyquist waveforms
having positive and negative polarities and staggered in time.
5. A magnetic recording and reproducing method according to claim 4
wherein step (a) further comprises passing the reproduced output
waveform through an automatic gain controller and a low pass filter
to the phase discrimination transversal equalizer.
6. A magnetic recording and reproducing apparatus for reproducing a
digitally recorded signal by using a phase discriminator, said
apparatus comprising:
a phase discrimination transversal equalizer for transforming a
reproduced output waveform of a magnetic head corresponding to an
isolated magnetization reversal to a dy-bit waveform which is a
waveform for a zero-crossing detection; and
a signal processing circuit for discriminating a zero-crossing
point of said dy-bit waveform as bit "1";
wherein said phase discrimination transversal equalizer includes a
signal processing circuit for adding a plurality of Nyquist
waveforms having positive and negative polarities and staggered in
time.
7. A magnetic recording and reproducing apparatus according to
claim 6 further comprising an automatic gain controller and a low
pass filter for applying the reproduced output waveform to the
phase discrimination transversal equalizer.
8. A magnetic recording and reproducing method for reproducing a
digitally recorded signal by using a phase discrimination system,
said method comprising the steps of:
(a) transforming a reproduced output waveform corresponding to an
isolated magnetization reversal reproduced by a magnetic head to a
dy-bit waveform which is a waveform for a zero-crossing detection
with a first phase discriminating transversal equalizer without
using a differentiation circuit, to produce a Nyquist waveform
having such a tap interval that a bit interval after the modulation
is equal to T;
(b) delaying the output waveform of said first equalizer by 2T;
(c) adding two Nyquist waveforms before and after the delaying of
step (b) with opposite polarities with a second phase
discrimination transversal equalizer to produce a zero-crossing
detection waveform; and
(d) discriminating the zero-crossing point as bit "1".
9. A magnetic recording and reproducing method according to claim
8, further comprising adding the 2T-delayed output waveform of step
(b) with one-half tap coefficient for adjacent taps to a center tap
of the Nyquist waveform of step (a) to produce a gating
waveform.
10. A magnetic recording and reproducing method according to claim
8, wherein step (a) comprises automatically producing the Nyquist
waveform with a phase discrimination automatic equalizer.
11. A magnetic recording and reproducing method according to claim
10, wherein step (a) further comprises equalizing the reproduced
waveform to produce one transversal Nyquist waveform having such a
tap interval that a bit interval after the modulation is equal to T
such that an amplitude sequence at the bit interval T in the
reproduced waveform corresponding to an isolated magnetization
reversal is "1, 0, -1".
12. A magnetic recording and reproducing method according to claim
11, wherein step (a) further comprises using a one-to-seven
modulation method in which a minimum zero run length is one.
13. A magnetic recording and reproducing apparatus for reproducing
a digitally recorded signal by using a phase discriminator, said
apparatus comprising:
a first signal processing circuit, including an automatic gain
controller and a low pass filter, for receiving a reproduced output
waveform of a magnetic head corresponding to an isolated
magnetization reversal;
a phase discrimination transversal equalizer for transforming the
reproduced waveform to a dy-bit waveform which is a waveform for a
zero-crossing detection, said phase discrimination transversal
equalizer including a first phase discrimination transversal
equalization circuit for producing a Nyquist waveform having such a
tap interval that a bit interval after the modulation is equal to
T, delay means for delaying the output waveform of said equalizer
by 2T, and a second phase discrimination transversal equalization
circuit for adding two Nyquist waveforms before and after said
delay means with opposite polarities to produce a zero-crossing
detection waveform; and
a second signal processing circuit for discriminating a
zero-crossing point of said dy-bit waveform as a bit "1".
14. A magnetic recording and reproducing apparatus according to
claim 13, further comprising a third phase discrimination
transversal equalization circuit for adding the 2T-delayed output
waveform with one-half tap coefficient for adjacent taps to a
center tap of the undelayed Nyquist waveform to produce a gating
waveform.
15. A magnetic recording and reproducing apparatus according to
claim 14, wherein said first phase discrimination transversal
equalization circuit is a phase discrimination automatic equalizer
for automatically producing the Nyquist waveform.
16. A magnetic recording and reproducing apparatus according to
claim 15, wherein one of said equalization circuits comprises an
automatic equalizer for producing one transversal Nyquist waveform
having such a tap interval that a bit interval after the modulation
is equal to T, and a signal processor for equalizing the signal
such that an amplitude sequence at the bit interval T in the
reproduced waveform corresponding to an isolated magnetization
reversal is "1, 0, -1".
17. A magnetic recording and reproducing apparatus according to
claim 16 further comprising a signal processing circuit for
performing a one-to-seven modulation method in which a minimum zero
run length is one.
18. A magnetic recording and reproducing method for reproducing a
digitally recorded signal by using a phase discrimination system,
said method comprising the steps of:
(a) applying a reproduced output waveform corresponding to an
isolated magnetization reversal reproduced by a magnetic head to a
first phase discriminating transversal equalizer to transform the
reproduced output waveform to a dy-bit waveform which is a waveform
for a zero-crossing detection;
(b) producing a Nyquist waveform having such a tap interval that a
bit interval after the modulation is equal to T;
(c) delaying the output waveform of said first equalizer by 2T;
(d) adding two Nyquist waveforms before and after the delaying of
step (c) with opposite polarities with a second phase
discrimination transversal equalizer to produce a zero-crossing
detection waveform; and
(e) discriminating the zero-crossing point as bit "1".
19. A magnetic recording and reproducing method according to claim
18 further comprising adding the 2T-delayed output waveform of step
(c) with one-half tap coefficient for adjacent taps to a center tap
of the undelayed Nyquist waveform of step (b) to produce a gating
waveform.
20. A magnetic recording and reproducing method according to claim
18, wherein step (b) comprises automatically producing the Nyquist
waveform with a phase discrimination automatic equalizer.
21. A magnetic recording and reproducing method according to claim
20, wherein step (b) further comprises equalizing the reproduced
waveform to produce one transversal Nyquist waveform having such a
tap interval that a bit interval after the modulation is equal to T
such that an amplitude sequence at the bit interval T in the
reproduced waveform corresponding to an isolated magnetization
reversal is "1, 0, -1".
22. A magnetic recording and reproducing method according to claim
21, wherein step (b) further comprises using a one-to-seven
modulation method in which a minimum zero run length is one.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording and
reproducing method for recording and reproducing digital
information and to an apparatus therefor, and more particularly to
a magnetic recording and reproducing method suitable for reshaping
a waveform by using an automatic equalizer in the reproduction of a
digitally recorded signal and to a recording and reproducing
apparatus for practising it.
In reproducing a recorded signal in a prior art magnetic recording
and reproducing apparatus, particularly a magnetic disk drive, a
phase discrimination system has been adopted. For example, in
JP-A-57-88511, a reproduced signal waveform is reshaped by two
equalizers to attain substantially perfect equalization, and then a
pulse corresponding to a peak of the reproduced signal is generated
by differentiation so that "1" and "0" are discriminated by the
presence or absence of the pulse. In JP-A-57-88511, it is assumed
that a zero-crossing point of the differentiated signal does not
shift if a shift of a peak point of the reproduced signal waveform
is eliminated by the use of a plurality of equalizers.
In JP-A-62-42368, an equalization constant in equalizing a
reproduced signal waveform is switched between an inner track and
an outer track of a magnetic disk, because degrees of interference
which the reproduced signal waveform receives differ between the
inner track and the outer track of the magnetic disk due to a
difference of a recording density.
SUMMARY OF THE INVENTION
However, in the prior art waveform equalization method in the
signal reproducing circuit, it is not possible to set an
equalization constant which principally renders a peak shift to
zero because, in the prior art, the zero-crossing pulse of the
waveform differentiated after the waveform equalization is
detected. It is assumed that discrimination times come at a
predetermined time interval, and zero-crossing of a peak of an
isolated waveform corresponding to one discrimination time is to be
detected. The isolated waveform is equalized by an equalization
constant which is considered optimum, and it is differentiated. In
the prior art, a peak shift of the isolated waveform derived from
the reproduced signal waveform may be adjusted by equalizing the
reproduced signal waveform by a plurality of equalizers or
preparing a plurality of equalization constants and selectively
using them. However, the inventors considered that the peak shift
is due to the amplitude shift of the zero-crossing point of the
differentiated output because the peak detection of the isolated
waveform corresponds to the zero-crossing point of the
differentiated output. Namely, the amplitude shift of the
zero-crossing point takes place when the differentiated output is
not zero at the phase discrimination point at which the peak of the
isolated waveform is to be detected. If only the isolated waveform
is involved, the differentiated output would be zero at the
discrimination time (peak point) but a small amplitude shift
appears due to the interference by other isolated waveforms. As a
result, in the reproduction of a continuous signal, it is not
possible to make an amplitude zero at each discrimination time
other than the zero-crossing time corresponding to the peak of the
isolated waveform, and the zero-crossing points vary in various
waveform patterns. In the prior art, the shift of the zero-crossing
point must be eliminated because it uses the differentiation. To
this end, it is necessary to set an equalization constant such that
the amplitude at each discrimination time is zero. However, taking
a variation of performance of a magnetic head and a magnetic disk
into consideration, it is very difficult to set a specific
equalization constant. Even if a plurality of equalization
constants are set and they are selectively used in accordance with
a radial position, it is practically impossible to control the peak
shift to zero.
It is an object of the present invention to provide a waveform
equalization method which makes a peak shift to zero in the signal
reproduction using a phase discrimination system, and an apparatus
for practising it. It is a more specific object of the present
invention to provide a method for eliminating the peak shift
without using a differentiation circuit for producing a zero
crossing pulse in the phase discrimination method and reshaping the
waveform, and a signal processing circuit for practising it.
In order to achieve the above objects, the present invention uses
the following means and method.
In a isolated waveform at a phase discrimination point
corresponding to an isolated magnetization reversal reproduced by
the magnetic head, automatic equalization is effected to make an
amplitude zero at each discrimination time other than a
zero-crossing point corresponding to recorded magnetization
reversal. To this end, instead of a differentiated waveform used in
the prior art phase discrimination method to produce the
zero-crossing pulse, the automatic equalization for amplitude
discrimination is effected to make the amplitude of the waveform
zero at each discrimination time other than the peak point to
produce a Nyquist waveform, and two such Nyquist waveforms of
opposite polarities are superimposed with an offset interval of two
bits to produce a waveform which is a substitute of the
differentiated waveform. As a result, the amplitude is zero at each
discrimination time other than the zero-crossing point in the
signal discrimination waveform and no peak shift takes place.
In accordance with the present invention, in a magnetic recording
and reproducing method for reproducing a digitally recorded signal
by the phase discrimination method, a reproduced output waveform
corresponding to isolated magnetization reversal reproduced by a
magnetic head is transformed to a zero-crossing detection waveform
by a phase discrimination transversal equalizer without using a
differentiation circuit, and the signal is processed by a circuit
which discriminates the zero-crossing point of the zero-crossing
detection waveform as a bit "1". There is provided a circuit for
producing a plurality of Nyquist waveforms having positive and
negative polarities derived from the reproduced output waveform
corresponding to the isolated magnetization reversal and adding the
waveforms staggered in time from each other, by the phase
discrimination transversal equalizer which reshapes it to the
zero-crossing detection waveform. Normally, a circuit for applying
a waveform passed through an automatic gain controller and a low
pass filter to the phase discrimination transversal equalizer is
provided.
In the signal recording and reproducing method of the present
invention, the signal is processed by using a first phase
discrimination transversal equalizer for producing a Nyquist
waveform having such a top interval that a bit interval after
modulation is equal to T, delay means for delaying an output
waveform from the equalizer by 2T, and a second phase
discrimination transversal equalizer for adding the two Nyquist
waveforms before and after the delay means in opposite polarities
to produce a zero-crossing isolated waveform.
In the present invention, a signal is processed by using a first
phase discrimination transversal equalizer for producing a Nyquist
waveform having such a tap interval that a bit interval after
modulation is equal to T, and a third phase discrimination
transversal equalizer for delaying the output waveform of the first
phase discrimination transversal equalizer by 2T, and adding three
waveforms with a center tap coefficient and one-half tap
coefficient for taps adjacent to a center tap, to produce a gating
waveform. The first phase discrimination transversal equalizer is
preferably a phase discrimination automatic equalizer which
automatically produces a Nyquist waveform.
The signal may be processed by using a single transversal Nyquist
waveform forming automatic equalizer having such a tap interval
that a bit interval after modulation is equal to T to equalize the
waveform such that a reproduced output waveform corresponding to
the isolated magnetization reversal is transformed to a waveform
with an amplitude sequence of "- - - , 0, 0, 1, 0, -1, 0, 0, - - -
" at the every bit interval T. A one-to-seven modulation method in
which a minimum value of a zero run length is "1" is preferably
used.
The magnetic recording and reproducing apparatus of the present
invention for reproducing a digitally recorded signal by using a
phase discrimination circuit comprises a phase discrimination
transversal equalizer for transforming a reproduced output waveform
of a magnetic head corresponding to the isolated magnetization
reversal to a zero-crossing detection waveform, and a signal
processing circuit for discriminating the zero-crossing point of
the zero-crossing detection waveform as bit "1".
The phase discrimination transversal equalizer has a signal
processing circuit for producing a plurality of Nyquist waveforms
with positive and negative polarities, derived from the reproduced
magnetization reversal and adding the waveforms after staggering in
time to produce a zero-crossing detection waveform. It may have a
signal processing circuit for applying a signal passed through an
automatic gain controller and a low pass filter to the phase
discrimination transversal equalizer.
Specifically, the magnetic recording and reproducing apparatus of
the present invention comprises a first phase discrimination
transversal equalizer for producing a Nyquist waveform having such
a tap interval that a bit interval after the modulation is equal to
T, delay means for delaying an output waveform of the equalizer by
2T, and a second phase discrimination transversal equalizer for
adding the two Nyquist waveform with opposite polarities before and
after the delay means to produce a zero-crossing detection
waveform.
In the application, it may comprise a third phase discrimination
three taps transversal equalizer for delaying the output waveform
of the first phase discrimination transversal equalizer by 2T, and
adding three waveforms with a center tap coefficient and one-half
tap coefficient for taps adjacent to a center tap, to produce a
gating pulse. The first phase discrimination transversal equalizer
is preferably a phase discrimination automatic equalizer which
automatically produces a Nyquist waveform. The equalizer may
comprise a single transversal Nyquist waveform forming automatic
equalizer having such a tap interval that a bit interval after the
modulation is equal to T to equalize the waveform such that a
reproduced output waveform corresponding to the isolated
magnetization reversal is transformed to a waveform with an
amplitude sequence of "- - - 0, 0, 1, 0, -1, 0, 0, - - - " at the
every bit interval T. It preferably comprises a signal processing
circuit for one-to-seven modulation in which a minimum value of a
zero run length is "1".
The signal processing circuit in the present invention may be an
integrated circuit, and the magnetic recording and reproducing
apparatus may be constructed by the integrated circuit.
As described above, instead of the differentiated waveform used in
the prior art phase discrimination method to produce the
zero-crossing pulse, the amplitude discrimination automatic
equalization is effected such that the amplitude of the waveform is
zero at each discrimination time other than the peak point to
produce a Nyquist waveform, and two Nyquist waveforms of opposite
polarities are superimposed with stagger of 2-bit intervals to
produce a waveform which is a substitution of the differentiated
waveform. As a result, the amplitude of the signal discrimination
waveform is zero at each discrimination time other than the
zero-crossing point and no peak shift takes place. Namely, the
zero-crossing pulse is produced like the differentiated waveform,
and the amplitude is zero at each discrimination time other than
the zero-crossing point so that the peak shift can be perfectly
eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram illustrating reproduced signal
processing of the present invention,
FIGS. 2A-2C illustrate a principle of the magnetic recording and
reproduction of the present invention,
FIG. 3 shows a configuration of a phase discrimination automatic
equalizer of a magnetic recording and reproducing apparatus of the
present invention,
FIG. 4 shows another configuration of the phase discrimination
automatic equalizer of the magnetic recording and reproducing
apparatus of the present invention,
FIG. 5 shows still another configuration of the phase
discrimination automatic equalizer of the magnetic recording and
reproducing apparatus of the present invention,
FIG. 6 shows a configuration of a phase discrimination circuit of
the magnetic recording and reproducing apparatus of the present
invention, and
FIG. 7 shows a block diagram of the magnetic recording and
reproducing apparatus of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention is now explained with
reference to the drawings.
FIG. 7 shows an overall configuration of a magnetic recording and
reproducing apparatus which uses the signal reproducing process of
the present invention. It comprises one or a plurality of magnetic
disks 79, a magnetic head slider 71 for mounting a magnetic head
arranged for each magnetic disk surface, an actuator 93 for driving
the magnetic head slider along the magnetic disk surface, a voice
coil motor 94 for driving the actuator, a recording and reproducing
amplifier 95, a control circuit 96 for controlling the switching of
a record/reproduce mode and the selection of the head, a circuit 97
for generating a record signal, and an interface circuit 91 for
interfacing with an external device and overall control. The
control circuit 96 instructs the selection of a reproducing head to
a reproduction selection circuit 98, and the reproduced signal is
transformed to data by a reproduction circuit 99. A servo signal
and a positioning control signal recorded on the magnetic disk
plane are processed by a positioning control circuit 90, which
controls the voice coil motor 94.
A principle of reproduced signal processing in the reproduction
circuit 99 of the present invention is now explained with reference
to FIGS. 2A-2C.
In the present embodiment, a one-to-seven modulation system is
adopted, and it is assumed that a bit interval after the modulation
is equal to T. Other modulation systems may be used to practice the
present invention so long as the bit interval after the modulation
is assured. FIG. 2A shows an output waveform 201 corresponding to
isolated magnetization reversal reproduced by the magnetic head 1
of FIG. 1.
In the present invention, in order to eliminate the zero-crossing
point shift of the differential output of the output waveform, a
waveform corresponding to the differentiated waveform of the prior
art is produced without using the differentiation process to detect
the zero-crossing point.
The waveform corresponding to the differentiated waveform is
produced in the following manner.
The output waveform 201 of the head is first transformed to a
Nyquist waveform h(t) 202 which has zero amplitude at a bit
interval T. Then, as shown in FIG. 2B, the Nyquist waveform h(t)
202 is delayed by a 2-bit (2T) period with the opposite polarity to
produce a Nyquist waveform -h(t-2T) 203, which is then added to the
Nyquist waveform h(t) 202 to produce a zero-crossing detection
waveform D(t)=h(t)-h(t-2T) 8 which is a substitution of the prior
art differentiated waveform. In the one-to-seven modulation system,
one-to-seven "0" bits always exist between "1" bits so that
adjacent bits are spaced by 2T or more. Accordingly, as shown in
FIG. 2B, if the amplitude is zero at each discrimination time
spaced by 2T or more from other, the zero-crossing point which
indicates a peak of a waveform pattern is not shifted and no peak
shift takes place whatever the wave pattern is. A gating waveform
E(t) 9 for extracting a zero-crossing pulse which exactly
corresponds to the magnetization reversal may be formed into a
waveform as shown in FIG. 2C. Namely, the gating pulse which does
not include adjacent zero-crossing point is formed. The
one-to-seven modulation system has been explained. Where another
modulation system is used, the zero-crossing detection waveform 8
and the gating waveform 9 may be formed while taking the run length
of the bit "1" and the bit "0" into consideration.
In the present invention, the above operation is attained by a
phase discrimination automatic equalizer 4.
FIG. 1 shows the reproduced signal processing components of the
magnetic recording and reproducing apparatus which uses the phase
discrimination automatic equalizer of the present invention. In
FIG. 1, a waveform reproduced by a magnetic head 1 is amplified by
an AGC (automatic gain controller) 2 and is passed through a LPF
(low pass filter) 3 to produce equalizer input waveform 7 with
reduced noise. It is then applied to a phase discrimination
automatic equalizer 4 to produce a peak shift-free zero-crossing
detection waveform 8 and a gating waveform 9, and reproduced data 6
is produced by a phase discriminator 5 to which waveforms 8 and 9
are applied. The magnetic head 1 may be either an inductive head or
an MR (magnetoresistive) head. The AGC 2 may be separate from a
pre-amplifier, and the order thereof with respect to the LPF 3 may
be reversed.
FIG. 3 shows a specific configuration of the phase discrimination
automatic equalizer 4. The equalizer input waveform 7 is applied to
a transversal equalizer 25 to produce a Nyquist waveform h(t) 202.
A tap coefficient C is automatically modified by a coefficient
correction unit 14 so that it is converged to an optimum
coefficient. An algorithm of the coefficient correction unit 14 may
use a well-known MSE (mean square error) method or ZF (zero
forcing) method. Information required for the coefficient
correction may differ from algorithm to algorithm so that the
wiring may be modified appropriately even if the wiring differs
from that shown. For example, the equalizer input waveform 7 is
essential in the MSE method, and the equalizer output waveform only
is sufficient in the ZF method. Identification data to be used by
the coefficient correction unit 14 may be determined by the
coefficient correction unit 14 or the phase discriminator 5. After
the Nyquist waveform 202 has been produced, it is delayed by 2-bit
periods and the zero-crossing waveform 8 and the gating waveform 9
are produced by the adders 12 and 13. The automatic equalizer 10 is
identical to the automatic equalizer for amplitude detection signal
processing frequently used in a communication field. FIG. 3 shows
an example of 5-tap amplitude, detection signal processing
automatic equalization, although the number of taps is determined
by a constraint of characteristics of the magnetic head and the
magnetic disk and a circuit scale, and the present invention does
not intend to limit the number of taps, and any number of taps may
be used. This is also true in the embodiments described below.
Another configuration of the phase discrimination automatic
equalizer 4 is shown in FIG. 4. The configuration of FIG. 4 is
essentially identical to that of FIG. 3 except for the coefficient
correction unit 14. The coefficient correction unit 14 of FIG. 4
determines a coefficient from the zero-crossing detection waveform
8. The coefficient is corrected such that the amplitude sequence of
the zero-crossing detection waveform 8 corresponding to the bit "1"
of the reproduced output waveform (isolated waveform) corresponding
to the isolated magnetization reversal is "1, 0, -1". The
coefficient may be determined from information of the gating
waveform 9, although this is not shown. In this case, the
coefficient is corrected such that the amplitude sequence of the
gating waveform 9 for the bit "1" of the isolated waveform is "0.5,
1, 0.5".
Another configuration of the phase discrimination automatic
equalizer 4 is shown in FIG. 5. In FIG. 5, the adder is of one
stage, and the zero-crossing detection waveform 8 and the gating
waveform 9 are produced in one time. Tap coefficients A and B are
set to have the following relation with a tap coefficient C of FIG.
3. ##EQU1##
In the present embodiment, the coefficient may be determined from
either information of the zero-crossing detection waveform 8 or
information of the gating waveform 9.
FIG. 6 shows a configuration of a phase discriminator 5 in the
present embodiment. The zero-crossing detection waveform 8 and the
gating waveform 9 are applied to limiters 15 and 16, respectively,
to produce a zero-crossing pulse 17 and a gating pulse 18. The
zero-crossing pulse 17 is then applied to a PLL (phase locked loop)
circuit 20 to establish a discrimination window 21. On the other
hand, only a correct read pulse 22 is extracted by the
zero-crossing pulse 17 and the gating pulse 18, and the reproduced
data 6 is discriminated as data "1" or "0" by a flip-flop 23. Only
a basic configuration of the phase discriminator 5 of the present
embodiment is shown, and various modifications may be made. For
example, while a simple AND gate is shown in a read pulse
extraction unit 24, preferential extraction of the read pulse may
be done by a flip-flop. Further, while only one slice level 19 is
shown in a generator of the gating pulse 18, a plurality of slice
levels may be used so that the read pulse extraction unit 24 can
extract the read pulse 22 more correctly.
In the magnetic recording and reproducing method which uses the
phase discriminator of the present invention, it is possible to
attain the zero peak shift, which has been difficult to attain in
the prior art, in the reproduced output waveform at the phase
discrimination point corresponding to the isolated magnetization
reversal, by only the phase discrimination transversal equalizer
without using the differentiation circuit, and the discrimination
reproduction performance in the magnetic recording and reproduction
is significantly improved. Accordingly, the recording density and
the reliability of the magnetic recording and reproducing apparatus
are improved.
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